This invention relates to improvements in infinitely variable transmissions and more particularly, it concerns an infinitely variable transmission unit adaptable for use in a mechanical power transmission system in a manner such that the range of the speed ratios available as a result of unit design is enlarged substantially in operation of the system.
Mechanical power transmissions which transmit torque from an input to an output at infinitely variable speed ratios are well known in the art and generally referred to as "I.V. transmissions". Because the power generating efficiency of most engines or prime movers is highest in only a limited range of operating speeds, I.V. transmissions have and continue to generate much interest as a potentially ideal solution to the transmission of power from a power source to a power-consuming load which must be driven at speeds varying from the operating speeds of the power source.
Mechanical I.V. transmissions are generally embodied in a structural organization capable of transmitting torque by friction between two or more traction surfaces on relatively rotatable bodies supported in such a manner as to enable the traction surfaces to be retained against one another under a normal force adequate to prevent slippage between the surfaces. The infinitely variable speed ratio is achieved by designing the torque arm or radius of one of the bodies to be continuously variable relative to the radius of the other body. The geometric configuration of two such bodies capable of attaining this result is exemplified by a wheel shiftable axially on a disc or a ring shiftable along the axis of a cone.
In a commonly assigned U.S. Pat. No. 4,152,946, issued May 8, 1979, in the name of the present inventor, several embodiments of infinitely variable transmissions are disclosed in which three frame supported working bodies operate to transmit a mechanical power input to a rotatable output at infinitely variable output/input speed ratios within the design range of the transmission. For purposes of definition in this background discussion as well as in the ensuing detailed description of the present invention and in the appended claims, the three working bodies may be termed respectively, an "alpha body" which is supported by the transmission frame for rotation on a first axis, a "beta body" which is concentric with a second axis inclined with respect to and intersecting the first axis at a point of axes intersection, and an "omega body" carried by the frame to be concentric with the first axis. Although both the omega body and the beta body may be rotatable on the respective axes with which they are concentric, it may be assumed for purposes of the present discussion that the omega body is held against rotation to provide a reaction torque whereas the beta body is rotatable on the second axis or journalled in the alpha body.
The infinitely variable speed ratio capability of such transmissions is achieved by providing one of the beta and omega bodies with a pair of rolling surfaces which are of revolution about the concentric body axis and which are of variable radii along that axis in symmetry with the point of first and second axes intersection. Physically, such rolling surfaces will thus provide the one body with a biconical-like configuration. The other of the beta and omega bodies is provided with a pair of rolling surfaces which are also of revolution about the concentric body axis but which are of relatively constant radius. The pairs of rolling surfaces on the beta and omega bodies are retained in frictional engagement with each other at two contact points or zones capable of positional adjustment to vary the ratio of the beta body surface radius (R.sub.b) to the omega body surface radius (R.sub.w). Thus, when an input torque is applied to the alpha body, causing it to rotate at a velocity .alpha. about the first axis, the beta body is carried in nutation by the alpha body and with the rolling surfaces thereof in torque transmitting contact with the rolling surfaces of the omega body. If the rotational speed of the beta body about the second axis is (.beta.) and the rotational speed of the omega body on the first axis is .omega., then the respective speeds of the three bodies are related by the equation: EQU .omega.-.alpha.+(.alpha.-.beta.)R.sub.b /R.sub.w =0
Because one of either the beta or the alpha body extends within the other of such bodies, the radius ratio R.sub.b /R.sub.w may represent a value of either less than 1 (where R.sub.b is always less than R.sub.w) or more than 1 (where R.sub.b is always greater than R.sub.w). If the function .rho. is accepted as designating either R.sub.b /R.sub.w or the reciprocal R.sub.w /R.sub.b, whichever is greater than 1, and the omega body is held against rotation as aforesaid so that .omega. equals 0, then the general equation of relative speeds is simplified to: EQU (.alpha.-.beta.).rho.-.alpha.=0
Also, where unit output is from the beta body, as it is when the omega body is retained against rotation on the first axis, the beta body is linked with an output shaft rotatable on the first axis by unit gearing originating with a pinion gear coupled for rotation with the beta body on the second axis and ending with a sun gear keyed for rotation with the unit output shaft. Such gearing may have a ratio factor (k) which theoretically may be of any value and also may be made either positive or negative depending on whether the unit gearing includes a reversing idler or not. In light of the foregoing, where .theta. is unit output speed and taking into account the unit gearing ratio (k), the output/input speed ratio of the unit is determined by the equation: EQU .theta./.alpha.=1-k.rho..
The state-of-the-art relating to I.V. transmissions and systems incorporating same is further developed to a point where speed ratio range of unit may be enlarged by external epicyclic gearing in which the I.V. unit input and output are used as two inputs to the external epicyclic gearing in a way to drive a single system output shaft from the epicyclic gearing. Such systems, moreover, have accounted for synchronous operation in which the system may be shifted between one range of infinitely variable speed ratios with adjustment of the I.V. unit in one direction between the extreme limits of its radius ratio, and a second contiguous range of system speed ratios in which the I.V. unit is adjusted in the opposite direction between its limits of speed ratio variation. In this respect, see U.S. Pat. No. 3,406,597, issued Oct. 22, 1968, to F. G. De Brie Perry, et al. While the use of such external epicyclic gearing to enlarge the speed ratio range available in an I.V. transmission unit represents a highly satisfactory solution to the problem of expanding the range of speed ratios available in an I.V. transmission, epicyclic gear operation is objectionable from the standpoint of introducing efficiency losses in the system. In other words, while synchronous operation of the I.V. transmission minimizes energy losses as a result of shifting between gearing ratio increments, the efficiency gain attained by such synchronous operation is offset by losses in external epicyclic gear operation.